MAGM 262

1
MAGM 262
Hydraulic Cylinders
Mr. Conrado
2
Hydraulic Cylinders

• Cylinders are basically linear actuators. Their
  outputs are straight line motion or force.
• The most common type of cylinders are single
  acting and double acting.
• The tubular housing is the cylinder body. Inside
  the cylinder body are the piston, piston seal and
  the rod.
• The bore refers to the inside diameter of the
  cylinder body
• The head end refers to the piston end of the
  cylinder.
• The rod end refers to the end from which the rod
  extends and retracts.

3
Single Acting Cylinder

• The single acting cylinder is often used on
  vertical lift gravity return operations.
• The control valve directs oil to the head end of
  the cylinder. The oil pressure acts upon the
  piston to extend the rod and lift the load.
• Gravity acting on the load is used to retract the
  rod and lower the load.

4
Double Acting Cylinder

• The most common of cylinders
• The National Fluid Power Association guidelines
  are used to standardize bore size, mounting
  styles, and overall dimensions.
• This allows cylinders to be interchangeable.

5
Effective Area of a Cylinder

• The bore size refers to the inside diameter of
  the cylinder. A cylinder with a large bore size
  has a larger effective area. This in turn
  increases the cylinders available force for a
  given pressure but decreases its speed for a
  given flow rate.
• The rod side of the piston has less effective
  surface area. This decreases the available force
  for the same given pressure but increases the
  piston travel speed.

6
Seals

• Different seals are used throughout the cylinder.
• The piston seal designed so that pressure
  expands the seal increasing pressure against the
  cylinder wall improving sealing force.
• The head seal (o-ring) prevents oil escaping
  between the rod gland and the cylinder wall.
• The rod seal is a U shaped seal that prevents
  oil escaping between the rod and the rod gland
  and wipes excess oil from the rod as it extends
  out from the cylinder.
• The wiper seal is fitted to the cylinder and
  prevents dirt and grit from being drawn into the
  cylinder as it retracts.
• Seals are made of polyurethane, nitrile, or
  nylon. The material should be verified to be
  compatible with the fluid used and the operating
  conditions.

7
Dampers

• When a moving cylinder runs into a dead end at
  the end of its stroke the concussion is called
  shock loading. Dampers (or Snubbers) are used to
  minimize or prevent shock loading.
• When the piston approaches full stroke, the
  damper moves into the return oil passage and
  restricts the return oil from the cylinder. This
  restriction causes an increase in the return oil
  pressure between the return oil passage and the
  piston. This oil pressure increase provides a
  cushion effect which slows the piston down and
  minimizes the shock that occurs.